Extended-nip press

ABSTRACT

An extended-nip press is disclosed comprising a press roll ( 2 ) and a backing roll ( 1 ), wherein the press roll ( 2 ) comprises a rotating endless-loop blanket ( 3 ) of a flexible, liquid-impervious material, a rigid and advantageously stationary roll support beam ( 4 ) that extends axially through the interior of the endless blanket ( 3 ), at least one shoe element ( 8 ) resting on the roll support beam ( 4 ) and having a concave top face, and loading means ( 6 ) for loading the shoe element ( 8 ) by way of pressing the concave top face thereof against the flexible endless-loop blanket ( 3 ) so as to make the blanket ( 3 ) form a press nip zone (N) in cooperation with the backing roll ( 1 ), said loading means ( 6 ) comprising a linear array of loading units ( 6′ ) aligned along the axial direction of the press roll ( 2 ), each one of the loading units comprising a functionally cooperating piston-cylinder unit. The invention is implemented by way of providing the piston ( 13 ) of said at least one piston-cylinder unit with a first end ( 14 ) which is adapted to enter at least partially into the bore of the cylinder ( 12 ) and to tilt relative to the cylinder ( 12 ) and, further, by providing said piston ( 13 ) of said at least one piston-cylinder unit with a second end ( 18 ) which is adapted to enter the piston mount ( 19 ) and to tilt relative to the piston mount, and, still further, by adapting the cylinder ( 12 ) of said at least one piston-cylinder movable between glide rails ( 21 ) aligned in the axial direction of the press roll ( 2 ) and is connected so as to load the endless-loop blanket ( 3 ) when a pressurized medium is introduced into the cylinder displacement space ( 15 ) formed between the piston ( 13 ) and the cylinder ( 12 ).

[0001] The present invention relates to an extended-nip press accordingto the preamble of the appended base claim.

[0002] Generally an extended-nip press comprises a press rollcooperating with a backing roll. Typically, the press roll comprises arotating endless-loop blanket of a flexible, liquid-impervious material,a rigid and advantageously stationary roll support beam that extendsaxially through the interior of the endless blanket, at least one pressshoe resting on the roll support beam and having a concave top face, andloading means for loading the shoe so as to press the concave top facethereof against the flexible endless blanket in order to form a pressnip zone in cooperation with the backing roll, whereby the loading meanscomprise a plurality of loading units adapted to operate as a lineararray in the axial direction of the press roll, each one of the loadingunit comprising a functionally cooperating piston-cylinder unit.

[0003] During the operation of an extended-nip press, the shoe issubjected to forces, typically occurring in the horizontal direction andchiefly oriented in the machine direction, that in this context arebroadly called frictional forces inasmuch they are caused by thefriction of the endless-loop blanket against the top face of the shoewhen the blanket passes the press zone. These frictional forces tend tomove and/or rotate the shoe in a manner that changes the mutualdisposition between the shoe and the backing roll and, hence, the nippressure profile of the press zone. In order to cancel the effect thethe displacement and/or rotation of the shoe due to the frictionalforces, the frictional forces imposed on the shoe must be transmitted tothe support structures of the extended-nip press.

[0004] A conventional arrangement for transmitting the frictional forcesfrom the shoe to the frame of the extended-nip press is such that on thetrailing edge of the shoe is provided a plurality of support membersbacking the shoe and giving the shoe a support against friction forcesimposed on the shoe. For instance, in patent publication FI 89286 isdisclosed an extended-nip press having a support bearing assemblyadapted to the outgoing side of the shoe for receiving the frictionalforces imposed on the shoe, the support bearing assembly including atleast one stationary support member connected to a support beam. Thedisadvantages of this arrangement have arisen from the horizontalsupport of the shoe that may be problematic in regard to the positionadjustment of the shoe by possibly restricting the degree of freedom inthe range of positions adjustable for the shoe. Moreover, these kinds ofconstructions have frequently been complicated which in turn isreflected in high manufacturing and service costs of the embodiment.Furthermore, smoothness of shoe loading has been problematic so that theshoe tends to stick at its trailing edge and service end.

[0005] It is an object of the extended-nip press according to theinvention to eliminate or at least reduce the above-described problemsrelated to the prior art.

[0006] It is a further object of the present invention to provide anextended-nip press, wherein the frictional forces imposed on the shoeare transmitted via at least one loading unit pressing the shoe to theroll support beam of the extended-nip press.

[0007] It is still further another object of the invention to provide anextended-nip press, wherein the loading units pressing the shoe arearranged so that the thermal expansion of the shoe cannot causesubstantial problems to the operation of the loading units.

[0008] To achieve the above-mentioned objects and others, theextended-nip press according to the invention is principallycharacterized by what is stated in the characterizing parts of theappended base claim.

[0009] The extended-nip press according to the present invention ischaracterized in that the piston of at least one piston-cylinder unitcomprises a first end which is adapted to enter the bore of the cylinderand to tilt relative to the center axis of the cylinder. The piston ofsaid piston-cylinder unit further comprises a second end which isadapted to enter the piston mount and to tilt relative to the centeraxis of the piston mount. The extended-nip press according to theinvention is still further characterized in that the cylinder of saidpiston-cylinder unit is adapted movable between glide rails aligned inthe axial direction of the press roll and connected so as to load theendless-loop blanket when a pressurized medium is introduced into thecylinder displacement space formed between the piston and the cylinder.

[0010] In a preferred embodiment of the extended-nip press according tothe present invention, the above-mentioned first end of the piston ismade at least partially globular. Such rounding of the piston's firstend allows the cylinder to tilt relative to the piston. Advantageously,the second end of the piston is adapted into the piston mount by meansof a spherical sliding bearing that allows the piston to tilt relativeto the mount. Inasmuch the first end of the piston is globular and thesecond end of the piston is adapted to rest in the piston mount on aspherical sliding bearing, the cylinder can move relative to the pistonmount irrespective of the tilting of the piston without a change (e.g.,by tilting) in the cylinder alignment. Furthermore, the above-describedpiston construction is advantageous in that structural changes due tothermal expansion cannot tilt the cylinder which remains orientedupright in spite of the tilting of the piston in the cylinder bore.

[0011] In another preferred embodiment of an extended-nip pressaccording to the present invention, the above-mentioned glide railsextend in a substantially contiguous fashion on both sides of the lineararray of the piston-cylinder units. This arrangement provides acontinuous glide surface that prevents the cylinder from moving in themachine direction, yet allowing the cylinder to move in the axialdirection of the press, that is, in the cross-machine direction.

[0012] In still another preferred embodiment of an extended-nip pressaccording to the present invention, key elements are adapted between atleast one piston-cylinder unit and at least one of the glide rails inorder to prevent said at least one piston-cylinder unit from moving inthe axial direction of the extended-nip press. Such advantageous keyedguidance of a cylinder or plural cylinders located close to the centerof the press allows thermal expansion of the shoe in either directionfrom the center line of the press during operation without causingproblems from thermal expansion to the operation of the press. Theunkeyed cylinders remain free to follow the movements of the thermallyexpanding/contracting shoe.

[0013] In a further another preferred embodiment of an extended-nippress according to the present invention, the shoe is connected to atleast one of the loading units in a fashion that allows the frictionalforces imposed on the shoe to be transmitted to the loading unit.Herein, the frictional forces imposed on the shoe can be transmitted tothe loading unit, e.g., using such a structure wherein the cylinder endloading the shoe is made at least partially spherical.

[0014] The frictional force received by the cylinder from the shoe isadvantageously transmitted to the roll support beam by providing atleast one of the piston-cylinder units with a force-transmitting surfacefacing the glide rail so as to transmit the frictional forces imposed onthe shoe to the roll support beam of the extended-nip press. By means ofthis arrangement, the frictional force imposed on the shoe istransmitted to the roll support beam via at least one piston-cylinderunit loading the shoe.

[0015] In a yet another preferred embodiment of an extended-nip pressaccording to the present invention, the linear array of loading units,advantageously their cylinders are adapted abut each other at leastpartially. As a result, the adjacent cylinders support each other so asto prevent the cylinders from tilting in the axial direction of press.

[0016] One of the greatest benefits of the extended-nip press accordingto the invention is its simple, yet extremely functional constructionallowing the press to be fabricated at a reasonable cost, whereby bothits maintenance and servicing is easy and fast. Furthermore, theextended-nip press according to the present invention is very durable inuse.

[0017] An additional benefit of the extended-nip press according to thepresent invention is its capability of transmitting the frictionalforces imposed on the shoe to the press frame, particularly to the rollsupport beam.

[0018] A still further benefit of the extended-nip press according tothe present invention is that it is not sensitive to malfunction orincorrect loading situations that may be induced by thermal expansion ofthe shoe during operation.

[0019] In the following, the invention is described in more detail bymaking reference to the appended drawings in which

[0020]FIG. 1 is a diagrammatic cross-sectional view of an extended-nippress as seen from the end of the press;

[0021]FIG. 2 is a diagrammatic cross-sectional view of an alternativeembodiment of an extended-nip press as seen from the long side of thepress, that is, a view taken in the machine direction of the press; and

[0022]FIG. 3 is a sectional view taken along plane A-A denoted in FIG.2.

[0023]FIG. 1 shows in a diagrammatic view exemplary embodiment of theconstruction of an extended-nip press as seen from the end of the press,that is, in a view in the cross-machine direction of the press. Theextended-nip press shown therein comprises an upper backing roll 1 and alower press roll 2 that define therebetween a press zone, later called apress nip N. The backing roll 1 may be a heated roll or an unheatedroll. The press roll 2 comprises an endless-loop blanket 3 made from aflexible and liquid-impervious material with a rigid, stationary rollsupport beam 4 extending axially through the interior of theendless-loop blanket. Furthermore, the press roll 2 comprises aplurality of loading means 5 that urge the blanket 3 toward the backingroll for forming the above-mentioned nip N in order to remove water froma web W passed through the nip. Herein, web refers to a paper orpaperboard web. The travel direction of the web passed into the nip isdenoted by an arrow in the diagram.

[0024] The loading means 5 include a loading unit 6 which is connectedto a roll support beam 4 and a shoe 8 that in turn is connected to theloading element via a saddle element 7 and is aligned parallel to thecenter axis of the press roll. The shoe element 8 is connected to thesaddle element by a key 9 inserted into both a keyway 10 made on thesurface of the shoe element facing the saddle element and a keyway 11made on the surface of the saddle element facing the shoe element. Thekey 9 transmits the frictional forces imposed on the shoe to the saddleelement.

[0025] The loading means 6 comprise a linear array of loading unitsaligned in a row in the axial direction of the press roll 2, one of theloading units being illustrated in FIG. 1. Each one of the loading unitscomprises a cylinder 12 and a piston 13 adapted to enter partially intothe bore of the cylinder so that at least the first end 14 of the pistonenters the displacement space 15 formed in the bore of the cylinder.

[0026] The first end 14 of the piston includes a seal element 16 servingto seal the side wall of the piston over the gap to the wall of thepressurized-medium receiving cylinder displacement space. As shown inthe diagram, the first end of the piston is partially rounded into aglobular shape at its periphery thus allowing the piston to tiltrelative to the cylinder when so required.

[0027] The other end 18 of the piston 13 is adapted by means of aspherical sliding bearing 20 into a piston mount 19 fitted on the rollsupport beam 4. The spherical sliding bearing facilitates the tilting ofthe piston relative the piston mount.

[0028] As shown in the diagram, the cylinder-piston combination forms afunctionally cooperative piston-cylinder combination, whereby theintroduction of a pressurized medium, such as hydraulic oil, via apassageway 17 of the pressurized medium into the cylinder displacementspace can be-used for elevating the operating pressure of the cylinderdisplacement space so as to move the piston relative to the cylinder.Inasmuch the means for passing a pressurized medium to thepressurized-medium passageway as well as the means for elevating thepressure of the pressurized medium or for controlling the flow thereofare well known to a person skilled in the art, they are omitted from thediagram. Having the second end 18 of the piston backed by the pistonmount 19, introduction of the pressurized medium into the cylinderdisplacement space will cause the cylinder to move outwardly relative tothe piston so as to load the shoe.

[0029] As shown in FIG. 1, facing each cylinder 12 on the incoming andoutgoing sides of the press are adapted glide rails 21 serving tosupport the cylinder in the machine direction of the press. The gliderails are connected by screws to the roll support beam 4. Being thussupported to the glide rails, the cylinder cannot tilt in the machinedirection when the cylinder is being actuated by the pressurized mediumintroduced into the cylinder displacement space. The surface of thecylinder remaining on the outgoing side of the press is provided with aforce-receiving surface 22 adapted to rest against the glide rail so asto transmit the frictional forces imposed on the shoe via the glide railto the roll support beam. An additional feature of the cylinder is thatits top surface is substantially spherical as drawn in the diagram.

[0030] The saddle element 7 is a planar component with its underside,that is, the surface facing the loading element, machined to incorporatea concave recess that after the saddle element is connected to theloading unit allows the spherical end surface of the loading unit andthis concave recess of the saddle element to form a ball joint allowingthe shoe element connected to the saddle element to rotate relative tothe loading unit. Also the frictional forces imposed on the shoe aretransmitted via this spherical end surface of the loading unit from thesaddle element to the loading unit.

[0031] The shoe element 8 shown in FIG. 1 is made from a suitable metalsuch as aluminum. The top surface of the shoe element opposed to thebacking roll has a concave cross section. The concave top surface mayalso be contoured to include a hydrodynamic pressure pocket.Alternatively, the pressure pocket may be designed to perform as ahydrostatic pressure pocket, whereby the shoe would additionallycomprise at least one line connection for feeding cooling/lubricatingoil into the pressure pocket. When the shoe is pressed against thebacking roll, the endless-loop blanket assumes a shape that isdetermined by the concave face of the shoe and by the curvature of thebacking roll adapted to cooperate with the press roll, whereby theblanket together with the backing roll defines a press zone throughwhich the paper or paperboard web can be passed to remove water from theweb.

[0032] In addition to those described above, an extended-nip pressincludes other parts and elements omitted from the diagrams for greaterclarity. These means are, e.g., means for feeding coolant and lubricantonto the top surface of the shoe, means for feeding pressurized mediuminto the cylinder acting as the loading element, etc. Furthermore, anextended-nip press may be implemented in an inverted fashion, wherebythe press roll is located above the backing roll.

[0033]FIG. 2 shows diagrammatically a partially cross-sectional view ofan extended-nip press as seen from the long side of the press. In FIG. 3is shown a sectional view taken along plane A-A denoted in FIG. 2. Thereference numerals used in FIGS. 2 and 3 are principally the same asthose of FIG. 1.

[0034] As shown in FIGS. 2 and 3, the contiguous shoe 8 is loaded bynine loading units 6 to press the endless-loop blanket 3 against backingroll 1. Obviously, the number of loading units in an extended-nip pressmay be varied so as to be a larger or a smaller number than used in theexemplifying embodiment. In practice, the number of loading unitsrequired is dictated by the width of the press and the desired controlprecision of the cross-machine nip pressure profile.

[0035] In the linear array of loading units, the cylinders placed in therow are arranged to partially abut each other. Due to this arrangement,the adjacent cylinders support each other so as to prevent the cylindersfrom tilting in the axial direction of the extended-nip press.

[0036] As shown in FIG. 3, between the loading unit 6′, which is locatedcentermost so as to situated at the center line of the press, and theguide rails 21 are adapted key elements 23 by means of which therespective loading unit is guided against tilting in the cross-machinedirection. As a result, run-time thermal expansion of the shoe may takeplace in either direction from the center line of the press withoutcausing problems in the operation of the press. The arrangement permitsthe unkeyed cylinders to move freely along with the expanding shoe.Obviously, even a greater number than one of the loading units may bekeyed in this fashion. Furthermore, the clamping of the loading unitsmay be accomplished by other means than using keys. For instance, atleast one of the glide rails may be contoured to have a recess at thelocation of the loading unit to be clamped. A still further benefit mustbe appreciated therein that a deflection of the roll structure will notbe reflected in the operation of the cylinders inasmuch the pistonsthereof can tilt as required.

[0037] It must be understood that the invention is not limited by theexemplary embodiment described above, but rather may be varied withinthe inventive spirit and scope of the appended claims.

What is claimed is:
 1. An extended-nip press formed by a press roll (2)and a backing roll (1), said press roll (2) comprising a rotatingendless-loop blanket (3) of a flexible, liquid-impervious material, arigid and advantageously stationary roll support beam (4) that extendsaxially through the interior of the endless blanket (3), at least oneshoe element (8) resting on the roll support beam (4) and having aconcave top face, and loading means (6) for loading the shoe element (8)by way of pressing the concave top face thereof against the flexibleendless-loop blanket (3) so as to make the blanket (3) form a press nipzone (N) in cooperation with the backing roll (1), said loading means(6) comprising a linear array of loading units (6′) aligned along theaxial direction of the press roll (2), each one of the loading unitscomprising a functionally cooperating piston-cylinder unit,characterized in that the piston (13) of said at least onepiston-cylinder unit comprises a first end (14) which is adapted toenter at least partially into the bore of the cylinder (12) and to tiltrelative to the cylinder (12), said piston (13) of said at least onepiston-cylinder unit further comprises a second end (18) which isadapted to enter the piston mount (19) and to tilt relative to thepiston mount, and the cylinder (12) of said at least one piston-cylinderunit is adapted movable between glide rails (21) aligned in the axialdirection of the press roll (2) and is connected so as to load theendless-loop blanket (3) when a pressurized medium is introduced intothe cylinder displacement space (15) formed between the piston (13) andthe cylinder (12).
 2. The extended-nip press of claim 1, characterizedin that said first end (14) of said piston is at least partiallyglobular.
 3. The extended-nip press of claim 1 or 2, characterized inthat said second end (18) of said piston is adapted to rest in thepiston mount (19) on a spherical sliding bearing (20).
 4. Theextended-nip press of any one of foregoing claims, characterized in thatsaid glide rails (21) extend in a substantially contiguous fashion onboth sides of the linear array of the piston-cylinder units.
 5. Theextended-nip press of any one of foregoing claims, characterized in thatkey elements (23) are adapted between said at least one piston-cylinderunit and at least one of the glide rails (21) in order to prevent saidat least one piston-cylinder unit from moving in the axial direction ofthe extended-nip press.
 6. The extended-nip press of claim 5,characterized in that key elements (23) are adapted between said atleast one piston-cylinder unit of the five centermost piston-cylinderunits, advantageously the selected piston-cylinder unit being thecentermost of them all, and at least one of the glide rails (21) inorder to prevent said at least one piston-cylinder unit from moving inthe axial direction of the extended-nip press.
 7. The extended-nip pressof any one of foregoing claims, characterized in that the shoe (8) isconnected to at least one loading unit (6′) so that the frictionalforces imposed on the shoe (8) are transmitted to said at least oneloading unit (6′).
 8. The extended-nip press of any one of foregoingclaims, characterized in that the end of the cylinder (12) loading theshoe is made at least partially spherical.
 9. The extended-nip press ofany one of foregoing claims, characterized in that the cylinder (12) ofsaid at least one piston-cylinder unit includes a force-receivingsurface (22) adapted to rest against the glide rail (21) so as totransmit the frictional forces imposed on the shoe (8) of theextended-nip press to the roll support beam (4) of the extended-nippress.
 10. The extended-nip press of any one of foregoing claims,characterized in that in said linear array of loading units (6′),advantageously their cylinders (12) are adapted abut each other at leastpartially.